Referring to FIG. 1, a prior art cable retainer used in a boat is illustrated. The prior art has a retaining seat 1 on a boat body A and a retaining block 2 assembled to the retaining seat 1. A lower center of the retaining seat 1 protrudes with an inserting rod 11 which can be inserted into the positioning hole A1 of the boat body A. A lower section of the inserting rod 11 has stoppers 12 for resisting against a lower end of the spring 13 enclosing the inserting rod 11. A top disk 10 of the retaining seat 1 has a penetrating hole 14 at a position coupling to a locking hole of the retaining block 2 for receiving an embedding stud P. The retaining block 2 receives the inserting rod 11 of the retaining seat 1. When the inserting rod 11 is received in the retaining block 2, the spring 13 encloses the lower end of the retaining seat 1. The lower end of the spring 13 resists against an upper side of the stopper 12 of the retaining seat 1. A top disk of the retaining block 2 resists on the top disk of the retaining seat 1. A top of the retaining block 2 has a plurality of tapered locking holes. Thereby, the penetrating hole 14 can be aligned to one of the locking holes so as to screw with the embedding stud P. Thus, the retaining seat 1 and retaining block 2 are fixed to a boat body A. The retaining seat 1 can be screw upwards so that a space is formed between the top disk of the retaining seat 1 and the top disk of the retaining block. The space serves to wind cables. Since in this prior art, the space can not be fixed, in winding or releasing the cable, the user must hold the cable retainer by one hand and release the cable by another hand. Thereby, the operation is tedious and inconvenient.